Conjunctivitis

1. Clinical Overview

Summary

Conjunctivitis is the inflammation of the conjunctiva, the thin transparent mucous membrane that covers the white of the eye (sclera) and lines the inner surface of the eyelids. It is the most common ocular diagnosis in primary care, accounting for approximately 1-2% of all general practitioner consultations and an estimated 6 million cases annually in the United Kingdom. [1,2,23] The classic clinical triad is redness, discharge, and ocular discomfort (grittiness or foreign body sensation), crucially presenting without significant pain or visual loss—features that distinguish simple conjunctivitis from sight-threatening conditions requiring urgent ophthalmology referral. [3,24]

Conjunctivitis is classified aetiologically into three main categories: bacterial (characterized by purulent discharge, typically caused by Staphylococcus aureus, Streptococcus pneumoniae, or Haemophilus influenzae), viral (characterized by watery discharge and preauricular lymphadenopathy, typically caused by adenovirus), and allergic (characterized by intense itching as the cardinal symptom, often seasonal). [4,25,26,27] The overwhelming majority of cases are self-limiting; bacterial conjunctivitis resolves in 5-7 days with or without treatment, while viral conjunctivitis may persist for 2-3 weeks. [5,25] Antibiotics shorten the duration of bacterial conjunctivitis by approximately 1 day (number needed to treat = 13), raising important questions about antibiotic stewardship in this common condition. [6,20]

The most critical clinical task is differentiating conjunctivitis from sight-threatening mimics including keratitis (corneal ulcer), uveitis (anterior chamber inflammation), acute angle-closure glaucoma, and scleritis. [7,23,24,32] Key discriminating features are visual acuity (should be normal), pain severity (mild grittiness only, not deep severe pain), photophobia (absent in simple conjunctivitis), and corneal clarity (should be clear). Special populations warrant urgent attention: neonates with ophthalmia neonatorum (gonococcal or chlamydial, notifiable disease), contact lens wearers (presumed Pseudomonas keratitis until proven otherwise), and immunocompromised patients (higher risk of severe or atypical infections). [8,28,29]

Key Facts

• Definition: Inflammation of the conjunctiva causing redness, discharge, and discomfort without pain or visual loss
• Prevalence: 1-2% of primary care consultations; lifetime prevalence approaches 100% [1]
• Annual Incidence: Approximately 6 million cases in the UK; 1-2% of the population per year [2]
• Most Common Cause: Viral (adenovirus) in adults; bacterial in children aged 1-5 years [4]
• Most Contagious Form: Viral (epidemic keratoconjunctivitis from adenovirus serotypes 8, 19, 37)
• Peak Demographics: All ages; bacterial peaks in children 1-5 years, allergic peaks in young adults 10-30 years
• Pathognomonic Feature for Allergic: Itch is the cardinal symptom—absence of itch makes allergy unlikely
• Gold Standard Investigation: Clinical diagnosis based on history and examination; swabs reserved for atypical/refractory cases
• First-line Treatment: Chloramphenicol 0.5% drops for bacterial; supportive care for viral; antihistamines for allergic
• Antibiotic Benefit: Shortens bacterial conjunctivitis by ~1 day; NNT 13 for early clinical cure [6]
• Self-Limiting Nature: Bacterial resolves in 5-7 days; viral in 2-3 weeks [5]
• Prognosis Summary: Excellent—most cases self-limiting with complete recovery and normal vision

Clinical Pearls

Diagnostic Pearl: "Pain vs Discomfort" — Conjunctivitis causes a gritty, burning, or "sand in the eye" sensation. It does NOT cause deep severe pain. True pain indicates involvement of the sclera (scleritis), cornea (keratitis), or iris (uveitis) and warrants urgent same-day ophthalmology referral.

Examination Pearl: "The Photophobia Test" — Shine a light in the uninvolved eye. If this causes pain in the red eye (consensual photophobia), this is uveitis (anterior chamber inflammation), NOT conjunctivitis. Conjunctivitis does not cause consensual photophobia because the anterior chamber is not inflamed.

Treatment Pearl: The Cochrane systematic review by Sheikh et al. (2012) demonstrated that most bacterial conjunctivitis is self-limiting and resolves in 5-7 days without treatment. Topical antibiotics provide modest benefit—shortening duration by approximately 1 day (RR 1.23, 95% CI 1.14-1.34, NNT 13). This evidence supports watchful waiting for mild cases and reinforces antibiotic stewardship. [6]

Pitfall Warning: Any red eye in a contact lens wearer is a corneal ulcer (Pseudomonas keratitis) until proven otherwise. DO NOT treat as simple conjunctivitis—remove lens immediately, refer to ophthalmology urgently (same day), and keep lens and case for culture. Pseudomonas can cause corneal perforation within 24 hours.

Differentiation Pearl: "Glued Eyes in the Morning" — Rietveld et al. (2004) found that eyelids glued together on waking (positive likelihood ratio 3.0) and absence of itching (negative likelihood ratio 0.2) are the best predictors of bacterial aetiology. [9] This simple clinical assessment guides appropriate antibiotic use.

Mnemonic: "RED EYE DANGER = Reduced vision, Extreme pain, Discharge purulent + severe, Eye contact lens use, Young neonate, Examining reveals corneal opacity, Deviation of pupil, Asymmetric pupils, No response to treatment in 7 days, Glaucoma symptoms (halos, nausea), Eyelid swelling severe (orbital cellulitis), Rash around eye (zoster)"

Why This Matters Clinically

Conjunctivitis is one of the most common presentations in primary care and emergency departments globally, making accurate diagnosis and management a core clinical skill. From an antimicrobial stewardship perspective, conjunctivitis represents a significant opportunity to reduce unnecessary antibiotic prescribing—evidence shows most cases are self-limiting, yet antibiotics are frequently prescribed due to patient expectation and diagnostic uncertainty. [10] The American Academy of Ophthalmology estimates that reducing unnecessary antibiotic use in conjunctivitis could prevent thousands of cases of antimicrobial resistance annually.

Delayed recognition of keratitis or uveitis can lead to permanent visual impairment or blindness. Contact lens-related Pseudomonas keratitis can progress to corneal perforation within 24-48 hours if not treated urgently. [11] Ophthalmia neonatorum (gonococcal or chlamydial conjunctivitis in newborns) is a notifiable disease in many jurisdictions and can cause rapid corneal perforation and permanent blindness if not diagnosed and treated promptly—gonococcal ophthalmia neonatorum can lead to corneal perforation within 24 hours. [12]

Allergic conjunctivitis significantly impacts quality of life and productivity during peak pollen seasons, with an estimated economic burden of billions annually in lost work days and healthcare costs. From a public health perspective, viral conjunctivitis outbreaks (epidemic keratoconjunctivitis) can affect schools, military barracks, healthcare facilities, and workplaces, requiring appropriate infection control measures including hand hygiene, surface disinfection, and temporary exclusion from communal settings. [13]

Trachoma (caused by Chlamydia trachomatis serovars A, B, C) remains the leading infectious cause of blindness globally, affecting 1.9 million people and endemic in 44 countries. The World Health Organization's SAFE strategy (Surgery, Antibiotics, Facial cleanliness, Environmental improvement) aims to eliminate trachoma as a public health problem by 2030. [14,30]

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2. Epidemiology

Incidence & Prevalence

• Annual Incidence: Approximately 1-2% of the population per year in developed countries [1,2]
• Primary Care Burden: Conjunctivitis accounts for 1% of all GP consultations in the UK (approximately 600,000 consultations per year) [2]
• Emergency Department: Represents ~2-3% of all emergency department visits for ocular complaints
• Childhood Prevalence: Bacterial conjunctivitis peaks in children aged 1-5 years; studies estimate 1-4 episodes per child before school age
• Seasonal Variation: Allergic conjunctivitis peaks in spring/summer (tree, grass, weed pollens); viral conjunctivitis peaks in autumn/winter (concurrent with respiratory virus circulation)
• Outbreak Potential: Viral (adenoviral) conjunctivitis can cause epidemics in closed environments—attack rates reaching 40-60% of susceptible individuals
• Global Burden: Trachoma (endemic Chlamydia trachomatis) affects 136 million people in endemic areas and causes 1.9 million cases of blindness or visual impairment globally [14]

Demographics

Risk Factors

Non-Modifiable Risk Factors:

Modifiable Risk Factors:

Protective Factors:

Temporal Patterns

• Time of Year: Allergic—spring/summer (tree pollen March-May, grass pollen May-July, weed pollen July-September); viral—autumn/winter (October-March, concurrent with rhinovirus, influenza)
• Time of Day: Bacterial—symptoms often worst on waking (crusted lids from overnight discharge accumulation); allergic—worse during daytime allergen exposure
• Duration of Symptoms: Bacterial 5-7 days typical (with or without treatment); viral 2-3 weeks (often biphasic with initial improvement then recurrence); allergic variable (hours to months depending on ongoing exposure)
• Incubation Period: Viral 5-12 days (adenovirus); bacterial 1-3 days; allergic immediate (minutes to hours) upon exposure in sensitized individuals
• Contagious Period: Viral—up to 14 days from symptom onset (adenovirus can be shed for weeks); bacterial—48 hours after starting antibiotics or while discharge present

Outbreak Epidemiology

Viral conjunctivitis (particularly adenoviral epidemic keratoconjunctivitis) can cause significant outbreaks in closed communities:

• Schools and nurseries: Rapid spread due to close contact, shared toys, poor hand hygiene in young children; attack rates 30-50%
• Military barracks: Classic setting for epidemic keratoconjunctivitis (EKC); historically significant cause of military unit incapacitation
• Healthcare settings: Nosocomial transmission from contaminated ophthalmic equipment, tonometers, trial contact lenses, or healthcare worker hands; importance of proper instrument disinfection
• Swimming pools: "Swimming pool conjunctivitis"—adenovirus (waterborne) or Chlamydia trachomatis (contaminated water in endemic areas)
• Attack rate in outbreaks: Can reach 40-60% of susceptible individuals in closed environments [13]
• Secondary household transmission: 10-50% depending on hygiene measures; shared towels major risk factor
• Prevention in outbreaks: Hand hygiene (70% alcohol gel), isolation of symptomatic cases for 10-14 days, daily disinfection of high-touch surfaces with 1:10 bleach solution, avoiding shared towels/pillowcases

Special Populations

Neonates (Ophthalmia Neonatorum):

Ophthalmia neonatorum is conjunctivitis occurring in the first 28 days of life. It is a notifiable disease in many jurisdictions due to the risk of rapid corneal perforation and blindness, particularly with gonococcal infection. [12]

Global Epidemiology: Ophthalmia neonatorum incidence varies globally: 0.003% in developed countries with routine screening to 0.5% in areas with high STI prevalence. [12]

Immunocompromised Patients:

Contact Lens Wearers:

Key Point: Pseudomonas aeruginosa keratitis can progress to corneal perforation within 24 hours. Any contact lens wearer with red eye, pain, photophobia, or discharge must have lens removed and be referred to ophthalmology the same day. [11]

Elderly Patients (> 65 years):

• Higher rates of concurrent dry eye disease (meibomian gland dysfunction, aqueous deficiency)
• May have chronic blepharitis contributing to recurrent conjunctivitis
• Herpes zoster ophthalmicus more common (incidence increases with age)
• May present with less typical symptoms ("just feels a bit gritty" despite significant infection)
• Higher prevalence of ocular surface disease from systemic medications (anticholinergics, diuretics)
• Delayed healing and higher risk of complications

Pregnant Women:

• Chloramphenicol: Relatively contraindicated in pregnancy (theoretical risk of bone marrow suppression, "grey baby syndrome" near term); use fusidic acid 1% as first-line alternative
• Chlamydial conjunctivitis: Must be treated to prevent vertical transmission to neonate (ophthalmia neonatorum)
• Gonococcal conjunctivitis: Rare in pregnancy but requires urgent treatment (IV ceftriaxone) and partner notification
• Allergic conjunctivitis: Sodium cromoglicate safe in pregnancy; oral antihistamines (cetirizine, loratadine) considered safe
• General approach: Avoid topical steroids; prefer mechanical measures (cool compresses, lubricants); treat systemic infections to prevent neonatal transmission

Global Burden

Conjunctivitis and related conditions represent a significant global health burden:

• Trachoma (Chlamydia trachomatis serovars A, B, C): Leading infectious cause of blindness globally; 1.9 million people blind or visually impaired worldwide; endemic in 44 countries (predominantly Sub-Saharan Africa, Middle East, Asia-Pacific) [14]
• WHO SAFE Strategy: Surgery (trichiasis), Antibiotics (azithromycin mass drug administration), Facial cleanliness, Environmental improvement (water/sanitation)
• Goal: Elimination of trachoma as a public health problem by 2030 (WHO Global Trachoma Mapping Project)
• Ophthalmia neonatorum: Incidence 0.003-0.5% of live births depending on maternal STI prevalence and screening programs; remains significant cause of childhood blindness in developing countries without routine antenatal screening [12]
• Gonococcal ophthalmia neonatorum: Incidence varies 1:3,000 to 1:10,000 live births in developed countries with screening; much higher in areas without antenatal STI screening
• Economic impact: Allergic conjunctivitis causes estimated billions in lost productivity annually during peak pollen seasons; presenteeism and absenteeism from work/school
• Healthcare utilization: Conjunctivitis accounts for approximately 1% of all primary care consultations annually (UK data) [2]; represents 2-3% of emergency department visits for ocular complaints
• Antibiotic prescribing: Conjunctivitis is a leading cause of outpatient antibiotic prescriptions globally; studies estimate 60-80% of cases receive antibiotics despite most being viral or self-limiting bacterial [10]

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3. Aetiology & Pathophysiology

Aetiology

Bacterial Conjunctivitis (30-50% of cases in primary care):

Viral Conjunctivitis (40-60% of cases in community):

Allergic Conjunctivitis (10-20% of cases; higher in atopic populations):

Non-Infectious, Non-Allergic Causes:

• Dry eye disease (keratoconjunctivitis sicca): Chronic ocular surface inflammation from tear film instability
• Chemical/Toxic: Silver nitrate (neonatal prophylaxis), chlorine (swimming), topical medications (preserved drops), cosmetics
• Mechanical: Foreign body, trichiasis (inturned lashes), eyelid malposition (ectropion, entropion)
• Autoimmune: Stevens-Johnson syndrome, ocular cicatricial pemphigoid, Sjögren's syndrome
• Neoplastic: Conjunctival intraepithelial neoplasia, lymphoma, sebaceous gland carcinoma

Pathophysiology

Step 1: Initiating Event — Pathogen/Allergen Contact with Conjunctival Surface

The conjunctiva is a thin, transparent, non-keratinized stratified squamous epithelium that covers the anterior sclera (bulbar conjunctiva) and lines the inner surface of the eyelids (tarsal/palpebral conjunctiva). It is richly vascularized and contains mucin-secreting goblet cells, conjunctiva-associated lymphoid tissue (CALT), and accessory lacrimal glands.

Normal Defense Mechanisms:

• Tear film: Three-layered structure (outer lipid layer from meibomian glands, middle aqueous layer from lacrimal gland, inner mucin layer from goblet cells)
  • "Contains antimicrobial enzymes: lysozyme (disrupts bacterial cell walls), lactoferrin (iron-binding, bacteriostatic), lactoperoxidase, beta-lysin"
  • "Secretory immunoglobulin A (sIgA): Prevents bacterial adherence to epithelium"
  • Complement components and immunoglobulins
• Blinking: Mechanical clearance of debris and pathogens; spreads tear film; pumps tears into nasolacrimal duct (12-15 blinks per minute)
• Normal bacterial flora: Commensal organisms (Staphylococcus epidermidis, Corynebacterium species, Propionibacterium acnes) compete with pathogens

Breach of Defense:

• Bacterial infection: Bacterial adhesins (pili, fimbriae) bind to epithelial cell surface receptors; breach of normal flora allows pathogen colonization
• Viral infection: Adenovirus enters cells via coxsackie-adenovirus receptor (CAR); HSV via herpesvirus entry mediator (HVEM); viral replication causes cell lysis
• Allergic response: Allergen (pollen protein, dust mite antigen) cross-links IgE antibodies on mast cell surfaces in previously sensitized individuals

Step 2: Early Inflammatory Response (Hours)

Innate Immune Response (Bacterial/Viral):

• Pattern recognition: Toll-like receptors (TLRs) on conjunctival epithelial cells recognize pathogen-associated molecular patterns (PAMPs)
  • "TLR4: Recognizes lipopolysaccharide (LPS) from Gram-negative bacteria"
  • "TLR2: Recognizes peptidoglycan from Gram-positive bacteria"
  • "TLR3, TLR7, TLR9: Recognize viral nucleic acids"
• Cytokine release: Activated epithelial cells release pro-inflammatory cytokines:
  • IL-1β, IL-6, IL-8 (neutrophil chemoattractant), TNF-α
  • "Chemokines: CXCL8 (IL-8), CCL2 (MCP-1), CCL5 (RANTES)"
• Vascular response:
  • Vasodilation of conjunctival vessels (hyperaemia/redness) mediated by histamine, prostaglandins, nitric oxide
  • Increased vascular permeability → plasma exudation → oedema (chemosis)
  • Upregulation of adhesion molecules (ICAM-1, VCAM-1, selectins) on endothelial cells
• Leukocyte recruitment:
  • "Bacterial: Neutrophil infiltration predominates (drawn by IL-8); neutrophils phagocytose bacteria and release neutrophil extracellular traps (NETs)"
  • "Viral: Lymphocytes (CD4+ and CD8+ T cells) and macrophages predominate; natural killer (NK) cells contribute to early viral clearance"

Type I Hypersensitivity Response (Allergic):

• Sensitization phase (prior exposure): Allergen presented by dendritic cells to CD4+ T helper 2 (Th2) cells → IL-4, IL-5, IL-13 production → B cell class switching to IgE production → IgE binds to FcεRI receptors on mast cells and basophils
• Effector phase (re-exposure):
  • Allergen cross-links IgE on mast cell surface → mast cell degranulation
  • "Immediate release (minutes): Histamine, tryptase, chymase → vasodilation, increased permeability, smooth muscle contraction, nerve stimulation (itch)"
  • "De novo synthesis (hours): Prostaglandins (PGD2), leukotrienes (LTC4, LTD4, LTE4), platelet-activating factor (PAF) → sustained inflammation"
  • "Eosinophil recruitment: IL-5 from mast cells and Th2 cells recruits eosinophils → eosinophil degranulation releases major basic protein (MBP), eosinophil cationic protein (ECP), eosinophil peroxidase (EPO) → epithelial damage"

Step 3: Established Inflammatory Process (Days)

• Continuing leukocyte infiltration: Sustained chemokine gradient recruits neutrophils (bacterial), lymphocytes/macrophages (viral), eosinophils (allergic)
• Discharge production:
  • "Purulent (bacterial): Neutrophils + bacteria + fibrin → thick yellow/green discharge"
  • "Serous/watery (viral): Plasma exudate with minimal cellular component → clear watery discharge"
  • "Mucoid (allergic): Goblet cell hypersecretion + eosinophils + mucus → thick stringy discharge"
• Goblet cell response: Inflammatory cytokines stimulate goblet cell proliferation and mucin hypersecretion
• Follicular vs Papillary Response (tarsal conjunctiva):
  • "Follicles (viral, chlamydial): Lymphoid hyperplasia; pale, dome-shaped, avascular mounds on tarsal conjunctiva; represent germinal centres (B cell proliferation)"
  • Papillae (bacterial, allergic): Vascularized (central vessel in each papilla), red, "cobblestone" appearance; represent hyperplasia of connective tissue with inflammatory cell infiltration
  • "Giant papillae (> 1 mm): Seen in vernal keratoconjunctivitis, atopic keratoconjunctivitis, giant papillary conjunctivitis; Type IV hypersensitivity component"
• Corneal involvement (typically spared in simple conjunctivitis, but may occur):
  • "Bacterial: Marginal keratitis (immune-mediated peripheral corneal infiltrates); corneal ulcer if severe"
  • "Viral (adenovirus): Sub-epithelial infiltrates (SEIs) develop 7-14 days after onset; represent immune response to viral antigens; cause glare and reduced vision; may persist months to years"
  • "HSV: Dendritic ulcer (branching epithelial defect); fluorescein staining shows characteristic pattern"
  • "Allergic: Usually no corneal involvement; severe vernal keratoconjunctivitis may develop shield ulcers"

Step 4: Resolution Phase (Days to Weeks)

• Pathogen clearance: Immune system eliminates bacteria (phagocytosis) or virally infected cells (cytotoxic T cells)
• Switch to anti-inflammatory response:
  • Macrophage phenotype switch from M1 (pro-inflammatory) to M2 (anti-inflammatory)
  • "Production of anti-inflammatory cytokines: IL-10, TGF-β"
  • Apoptosis of infiltrating leukocytes
• Reduction in inflammatory mediators: Histamine, prostaglandins, leukotrienes metabolized and cleared
• Re-epithelialization: Conjunctival epithelial cells proliferate and migrate to restore normal architecture
• Restoration of tear film: Goblet cells return to baseline mucin production; tear film stability restored
• Resolution of hyperaemia: Vasoconstriction; reduced vascular permeability; resolution of oedema
• Timeline:
  • "Bacterial: Typically 5-7 days (with or without antibiotics); antibiotics shorten by ~1 day [5,6]"
  • "Viral: 2-3 weeks; often biphasic (initial symptoms improve, then recur before final resolution); adenovirus sub-epithelial infiltrates may persist months"
  • "Allergic: Hours to days after allergen removal; chronic if ongoing exposure"

Step 5: Complications (if occur)

• Corneal involvement: Progression to keratitis (bacterial ulcer, viral dendritic ulcer, adenovirus sub-epithelial infiltrates)
• Membrane/pseudomembrane formation: Severe viral (adenoviral) or bacterial (Streptococcus pyogenes, Corynebacterium diphtheriae); fibrinous exudate adheres to tarsal conjunctiva; risk of scarring and symblepharon (conjunctival adhesions)
• Scarring (symblepharon): Adhesion between bulbar and tarsal conjunctiva; restricts eye movement; seen after severe membranous conjunctivitis, chemical burns, autoimmune disease
• Chronic blepharoconjunctivitis: Ongoing lid margin (blepharitis) and conjunctival inflammation; requires long-term lid hygiene
• Secondary bacterial infection: Viral conjunctivitis may develop bacterial superinfection; change from watery to purulent discharge; consider antibiotics
• Systemic spread (rare): Gonococcal dissemination (arthritis, endocarditis); neonatal HSV dissemination (encephalitis, hepatitis)
• Trichiasis and entropion: Late complication of trachoma; inturned lashes abrade cornea leading to scarring and blindness [14]

Molecular Pathophysiology (Advanced)

Exam Detail: Adenovirus Replication and Immune Evasion:

Adenovirus is a non-enveloped, double-stranded DNA virus. Serotypes 8, 19, and 37 cause epidemic keratoconjunctivitis (EKC); serotypes 3, 4, and 7 cause pharyngoconjunctival fever (PCF).

1. Viral entry: Fiber protein binds to coxsackie-adenovirus receptor (CAR) on epithelial cells; penton base interacts with αvβ3 and αvβ5 integrins → receptor-mediated endocytosis
2. Replication: Viral DNA enters nucleus; hijacks host cell transcription/translation machinery; produces ~10,000 viral particles per cell
3. Cell lysis: Adenovirus death protein (ADP) causes cell lysis; release of viral particles and danger-associated molecular patterns (DAMPs)
4. Immune response: Released viral antigens trigger CD8+ cytotoxic T cell response; sub-epithelial infiltrates (SEIs) represent deposition of immune complexes and infiltration of T cells 7-14 days post-infection
5. Persistence: Adenovirus can establish latent infection in lymphoid tissue; may reactivate in immunosuppression

Type I Hypersensitivity Molecular Cascade:

1. IgE cross-linking on mast cells: Conformational change in FcεRI → activation of Lyn and Syk tyrosine kinases
2. Signal transduction: Activation of phospholipase C (PLC) → IP3 (mobilizes intracellular Ca2+) and DAG (activates protein kinase C)
3. Degranulation: Ca2+ influx triggers fusion of granules with plasma membrane → release of preformed mediators (histamine, tryptase, heparin)
4. Histamine effects:
   • H1 receptors on blood vessels → vasodilation, increased permeability
   • H1 receptors on sensory nerves → itch sensation
   • H1 receptors on goblet cells → mucus secretion
5. Arachidonic acid metabolism:
   • Phospholipase A2 cleaves membrane phospholipids → arachidonic acid
   • Cyclooxygenase pathway → prostaglandin D2 (PGD2) → vasodilation, chemotaxis
   • Lipoxygenase pathway → leukotrienes (LTC4, LTD4, LTE4) → bronchoconstriction, increased vascular permeability, eosinophil recruitment
6. Late-phase response (4-8 hours): Eosinophil infiltration → release of major basic protein (MBP), eosinophil cationic protein (ECP) → epithelial damage and sustained inflammation

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4. Clinical Presentation

Symptoms

Cardinal Symptoms (Typical Presentation):

• Redness (hyperaemia): Present in 95-100% of cases; bilateral or unilateral initially; may spread to fellow eye in 1-2 days
• Discharge: Character guides aetiology
  • "Purulent (thick, yellow/green, sticky): Bacterial"
  • "Watery/serous (clear, profuse): Viral"
  • "Stringy mucoid (thick, ropy): Allergic"
• Ocular discomfort: Grittiness, foreign body sensation, burning (80-90% of cases)
  • "Key Point: This is discomfort, NOT severe pain. Deep severe pain indicates cornea (keratitis), sclera (scleritis), or anterior chamber (uveitis) involvement → urgent referral"
• Crusting of eyelids: Particularly on waking in bacterial conjunctivitis; lids "stuck together" in morning (positive predictive value for bacterial aetiology) [9]
• Itching: Cardinal symptom of allergic conjunctivitis; absence of itch makes allergy unlikely (negative likelihood ratio 0.2) [9]
• Tearing (epiphora): Reflex tearing from ocular surface irritation
• Eyelid swelling: Mild puffiness common; severe swelling suggests orbital cellulitis (requires urgent referral)

Associated Symptoms:

• Viral: Upper respiratory tract infection symptoms (sore throat, rhinorrhoea, cough) in pharyngoconjunctival fever; tender preauricular or submandibular lymphadenopathy
• Allergic: Concurrent allergic rhinitis (sneezing, nasal discharge), atopic dermatitis
• Bacterial: May have concurrent otitis media (especially children with H. influenzae or S. pneumoniae)

Symptoms that Suggest Alternative Diagnosis (Red Flags):

• Severe pain: Keratitis, scleritis, acute angle-closure glaucoma, uveitis
• Photophobia (especially consensual): Uveitis, keratitis
• Reduced visual acuity: Keratitis, uveitis, acute glaucoma (conjunctivitis should NOT affect vision)
• Halos around lights: Acute angle-closure glaucoma
• Headache, nausea, vomiting: Acute angle-closure glaucoma
• Unilateral severe purulent discharge with rapid onset: Gonococcal conjunctivitis (hyperacute bacterial)
• Vesicular rash on forehead/nose: Herpes zoster ophthalmicus

Signs

General Signs by Aetiology:

Specific Examination Findings:

External Examination:

• Eyelids: Crusting (bacterial), swelling (viral, allergic, severe bacterial), vesicles (HSV, VZV)
• Periorbital skin: Dermatitis (atopic), vesicular rash in V1 distribution (herpes zoster ophthalmicus)
• Lymph nodes: Preauricular (palpate anterior to tragus)—tender and enlarged in viral conjunctivitis (50% of cases)

Conjunctival Examination:

• Injection pattern:
  • "Diffuse (entire conjunctiva uniformly red): Conjunctivitis"
  • "Ciliary flush (redness concentrated around corneal limbus): Uveitis, keratitis (suggests anterior chamber or corneal involvement → urgent referral)"
  • "Sectoral (localized area of redness): Episcleritis, subconjunctival haemorrhage, pterygium"
• Discharge: Assess character (purulent, watery, mucoid); sample for culture if indicated (see Investigations)
• Chemosis (conjunctival oedema): Marked in allergic conjunctivitis; appears as "jelly-like" swelling; may prolapse over lid margin
• Subconjunctival haemorrhage: May occur with viral (adenovirus) or severe bacterial conjunctivitis; benign; reassurance

Tarsal Conjunctiva (Evert Upper Lid):

Critical examination skill—often omitted but provides key diagnostic information:

• Follicles: Pale, dome-shaped, avascular elevations; represent lymphoid hyperplasia
  • "Seen in: Viral (adenovirus), chlamydial (inclusion conjunctivitis, trachoma), toxic (chronic topical medication use)"
• Papillae: Red, "cobblestone" appearance with central vessel in each papilla; represent vascularized connective tissue hyperplasia
  • "Small papillae (less than 1 mm): Bacterial, allergic (SAC, PAC)"
  • "Giant papillae (> 1 mm): Vernal keratoconjunctivitis (VKC), atopic keratoconjunctivitis (AKC), giant papillary conjunctivitis (GPC from contact lenses)"
• Membrane/pseudomembrane: Fibrinous exudate on tarsal conjunctiva
  • "Pseudomembrane (easily peeled off without bleeding): Adenovirus, Streptococcus"
  • "True membrane (bleeds when peeled): Corynebacterium diphtheriae (rare), severe adenovirus"

Corneal Examination:

• Clarity: Should be completely clear in simple conjunctivitis; any opacity requires urgent ophthalmology referral
• Fluorescein staining (instill fluorescein drop; examine with blue light):
  • "Normal: No staining (intact epithelium)"
  • "Punctate epithelial erosions (PEE): Superficial punctate keratitis (SPK); seen in viral, dry eye, blepharitis; fine scattered dots"
  • "Dendritic ulcer: Branching epithelial defect with terminal bulbs; pathognomonic for HSV keratitis; requires urgent ophthalmology and topical acyclovir"
  • "Geographic ulcer: Large irregular epithelial defect; VZV or severe HSV"
  • "Corneal ulcer: White/grey opacity with overlying epithelial defect; bacterial keratitis; medical emergency"
• Sub-epithelial infiltrates (SEIs): Hazy white spots in anterior stroma; develop 7-14 days after adenoviral conjunctivitis; may persist months/years; cause glare and photophobia

Pupil Examination:

• Size, shape, reactivity: Should be normal and equal in conjunctivitis
• Abnormalities suggest alternative diagnosis:
  • "Small, irregular, poorly reactive: Anterior uveitis (iritis)"
  • "Mid-dilated, fixed, non-reactive: Acute angle-closure glaucoma"
  • "Relative afferent pupillary defect (RAPD): Optic nerve pathology (optic neuritis, severe glaucoma)"

Visual Acuity:

• MUST be tested and documented in all cases of red eye
• Expected in conjunctivitis: Normal (6/6 or 20/20)
• Reduced acuity suggests:
  • Keratitis (corneal involvement)
  • Uveitis (anterior chamber inflammation)
  • Acute glaucoma (corneal oedema, optic nerve ischaemia)
  • Adenovirus sub-epithelial infiltrates (reduced vision, glare)
• Any reduction in visual acuity warrants urgent ophthalmology referral

Red Flags — Urgent/Emergency Referral Criteria

[!CAUTION] RED FLAGS — Seek immediate same-day ophthalmology review if ANY of the following present:

• Severe pain (not just mild grittiness)—suggests keratitis, scleritis, or acute glaucoma
• Photophobia, especially consensual photophobia (light in uninvolved eye causes pain in red eye)—suggests anterior uveitis
• Reduced visual acuity on Snellen testing—suggests corneal or intraocular involvement
• Contact lens wearer with red eye—assume Pseudomonas keratitis until proven otherwise; same-day ophthalmology referral mandatory [11]
• Corneal opacity or white spot—bacterial/viral/fungal keratitis; requires urgent corneal scraping and treatment
• Pupil abnormality (fixed, irregular, mid-dilated, RAPD)—acute glaucoma or uveitis
• Hypopyon (pus layering in inferior anterior chamber)—severe bacterial keratitis or endophthalmitis
• Neonatal conjunctivitis (first 28 days of life)—ophthalmia neonatorum; gonococcal can perforate cornea within 24 hours; emergency referral [12]
• Severe purulent discharge with rapid onset (hyperacute)—gonococcal conjunctivitis; requires systemic antibiotics
• Ciliary flush (redness concentrated around corneal limbus)—suggests anterior chamber or corneal pathology
• No improvement after 7 days of appropriate treatment—consider resistant organism, viral cause, or alternative diagnosis
• Worsening at any time during treatment—suggests progression or incorrect diagnosis

Differential Diagnosis

The "red eye" differential is critical—missing sight-threatening conditions can lead to permanent visual loss.

Clinical Approach to Red Eye Differentiation:

1. Visual acuity: Normal → likely conjunctivitis; reduced → keratitis/uveitis/glaucoma
2. Pain severity: Mild/gritty → conjunctivitis; severe → keratitis/uveitis/glaucoma/scleritis
3. Photophobia: Absent → conjunctivitis; present → uveitis/keratitis
4. Pupil: Normal → conjunctivitis; abnormal → uveitis/glaucoma
5. Cornea: Clear → conjunctivitis; opacity/infiltrate → keratitis
6. Discharge: Present → conjunctivitis; absent → consider other causes

---

5. Investigations

Bedside/Point-of-Care Tests

Laboratory Tests

Indications for Conjunctival Swab/Culture:

Conjunctivitis is a clinical diagnosis in the vast majority of cases. Microbiological investigation is NOT routinely required. Reserve swabs for specific indications:

Sampling Technique for Conjunctival Swab:

1. Avoid topical anaesthetic (may inhibit bacterial growth) if possible; if needed, instill and wait 30 seconds before swabbing
2. Avoid contact with lid margin (contaminants from skin flora)
3. Evert lower lid; gently swab lower conjunctival fornix (cul-de-sac) with rolling motion
4. Place swab in transport medium (charcoal or Stuart's medium for bacterial culture; viral transport medium for viral PCR)
5. Send to laboratory promptly (within 4 hours if possible; refrigerate if delay > 4 hours)
6. Specify tests required: Bacterial culture and sensitivity; chlamydia/gonorrhoea NAAT; viral PCR (adenovirus, HSV, VZV)

Expected Laboratory Findings:

Note: Culture sensitivity for bacterial conjunctivitis is only 60-80% (many cases culture-negative despite clinical bacterial infection). [10]

Imaging

Imaging is NOT routinely required for conjunctivitis. Specialist ophthalmology investigations may include:

Diagnostic Criteria

Clinical Diagnostic Criteria for Conjunctivitis (based on NICE Clinical Knowledge Summaries and Royal College of Ophthalmologists guidelines):

A diagnosis of simple conjunctivitis requires ALL of the following:

1. ✅ Red eye (conjunctival injection)
2. ✅ Discharge (purulent, watery, or mucoid)
3. ✅ Gritty sensation or foreign body sensation (NOT severe pain)
4. ✅ Normal visual acuity (Snellen testing)
5. ✅ Normal pupil (size, shape, reactivity)
6. ✅ Clear cornea (no opacity on direct inspection; fluorescein staining shows no ulcer)
7. ✅ No photophobia (or minimal discomfort with light, not true photophobia)

If ANY criterion is NOT met → Consider alternative diagnosis and refer to ophthalmology

Specific Diagnostic Criteria:

Bacterial Conjunctivitis:

• Purulent discharge (yellow/green, sticky)
• Eyelids glued together on waking (positive predictive value for bacterial) [9]
• Absence of itching (negative predictive value for allergic) [9]
• May be unilateral initially → bilateral in 24-48 hours

Viral Conjunctivitis:

• Watery discharge
• Preauricular lymphadenopathy (tender, palpable)
• Follicles on tarsal conjunctiva (lid eversion)
• Associated upper respiratory tract infection symptoms
• Highly contagious (household/close contact spread)

Allergic Conjunctivitis:

• Itch is cardinal symptom (absence makes allergy unlikely)
• Bilateral simultaneous onset
• Stringy mucoid discharge
• Chemosis (conjunctival oedema)
• Papillae on tarsal conjunctiva
• Seasonal pattern or allergen exposure history
• Concurrent allergic rhinitis or atopic dermatitis

Ophthalmia Neonatorum (neonatal conjunctivitis, age less than 28 days):

• Onset 2-5 days → suspect Neisseria gonorrhoeae (hyperacute, copious purulent discharge; emergency)
• Onset 5-14 days → suspect Chlamydia trachomatis (mucopurulent; may have pneumonitis)
• Requires swab + NAAT, urgent ophthalmology referral, systemic antibiotics [12]

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6. Management

Management Algorithm

                      RED EYE PRESENTATION
                             ↓
┌────────────────────────────────────────────────────────────────┐
│                    INITIAL ASSESSMENT                           │
│  • Visual Acuity (MANDATORY—test with Snellen chart)           │
│  • Check for RED FLAGS:                                         │
│    - Severe pain (NOT mild grittiness)                          │
│    - Photophobia (especially consensual)                        │
│    - Reduced visual acuity                                      │
│    - Contact lens wearer                                        │
│    - Corneal opacity or white spot                              │
│    - Pupil abnormality (irregular, fixed, RAPD)                 │
│    - Neonate (less than 28 days old)                                     │
│    - Hypopyon (pus in anterior chamber)                         │
└────────────────────────────────────────────────────────────────┘
                             ↓
      ┌──────────────────────┼──────────────────────┐
      ↓                      ↓                      ↓
  RED FLAGS              NO RED FLAGS           NEONATE
  PRESENT?                                     (less than 28 days)
      ↓                      ↓                      ↓
  **URGENT**            Assess Discharge        **EMERGENCY**
  OPHTHALMOLOGY         and Features            OPHTHALMOLOGY
  REFERRAL                   ↓                  REFERRAL
  (same day)    ┌───────────┼───────────┐      (Ophthalmia
      │         ↓           ↓           ↓       Neonatorum)
      │     PURULENT     WATERY       ITCHY         │
      │     Thick        Clear        Stringy       │
      │     yellow/      serous       mucoid        │
      │     green        discharge    discharge     │
      │     Stuck lids   Preauricular  Chemosis     │
      │     on waking    lymph node   Bilateral     │
      │         ↓           ↓           ↓            │
      │     BACTERIAL    VIRAL       ALLERGIC       │
      │         ↓           ↓           ↓            │
      │  Chloramphenicol Supportive  Antihistamine  │
      │  0.5% drops      Care:       /Mast Cell     │
      │  1 drop every    • Lubricants Stabilizer:   │
      │  2 hours for     • Cool       • Olopatadine │
      │  48h, then QDS     compress   • Azelastine  │
      │  for 5-7 days    • Hand       • Sodium      │
      │                    hygiene      cromoglicate│
      │  Alternative:    • No sharing • Allergen    │
      │  Fusidic acid      towels       avoidance   │
      │  1% (Fucithalmic)• Work/school• Oral        │
      │  BD for 7 days     exclusion    cetirizine/ │
      │  (preferred if     10-14 days   loratadine  │
      │  pregnant)                                   │
      ↓                                              ↓
┌────────────────────────────────────────────────────────────────┐
│                      FOLLOW-UP & SAFETY NETTING                 │
│  • No improvement in 7 days → Refer (consider swab)            │
│  • Worsening at any time → Refer urgently                      │
│  • Develop pain, photophobia, vision change → Emergency        │
│  • Advise hand hygiene, no sharing towels/cosmetics            │
│  • Work/school exclusion if viral (10-14 days from onset)      │
│  • Contact lens wearers: lens holiday until fully resolved     │
└────────────────────────────────────────────────────────────────┘

Acute/Emergency Management

Ophthalmia Neonatorum (Neonatal Conjunctivitis):

IMMEDIATE ACTIONS (this is a medical emergency, especially if gonococcal):

1. Urgent ophthalmology referral (same day; emergency if copious purulent discharge)
2. Saline lavage: Copious irrigation with sterile saline to clear discharge (prevents corneal contact and ulceration)
3. Swabs: Conjunctival swab for:
   • Bacterial culture and sensitivity (including gonococcal culture on chocolate agar/Thayer-Martin medium)
   • Chlamydia and gonorrhoea NAAT (nucleic acid amplification test)
   • Viral PCR if vesicles present (HSV)
4. Systemic antibiotics (DO NOT rely on topical alone):
   • Gonococcal: Ceftriaxone 25-50 mg/kg IV/IM (max 125 mg) single dose
   • Chlamydial: Erythromycin 12.5 mg/kg PO QDS for 14 days
5. Topical antibiotics: Erythromycin 0.5% ointment QDS (after lavage)
6. Notify: Ophthalmia neonatorum is a notifiable disease in many jurisdictions (UK, Australia)
7. Maternal and partner screening and treatment: STI screening and treatment; contact tracing [12]

Contact Lens-Related Keratitis (Presumed Pseudomonas):

IMMEDIATE ACTIONS (this can progress to corneal perforation within 24 hours):

1. Remove contact lens immediately; keep lens and case for culture (do NOT discard)
2. Same-day ophthalmology referral (emergency if severe pain, large infiltrate)
3. Do NOT treat as simple conjunctivitis
4. Do NOT prescribe topical antibiotics in primary care (requires corneal scraping and intensive topical antibiotics by ophthalmology)
5. Safety netting: Warn patient this is a sight-threatening emergency; attend ophthalmology immediately

Gonococcal Conjunctivitis (Hyperacute Bacterial in Adults):

• Rare in adults (sexually transmitted)
• Copious purulent discharge with rapid onset
• Risk of corneal perforation within 24-48 hours
• Management: Urgent ophthalmology referral; systemic ceftriaxone 1 g IM/IV stat; topical antibiotics (ofloxacin 0.3% hourly); saline lavage; STI screening and partner notification

Conservative Management

Applies to ALL types of conjunctivitis (adjunct to specific treatments below):

Medical Management

Bacterial Conjunctivitis:

Evidence for Antibiotic Use:

• Cochrane systematic review (Sheikh et al. 2012): 11 RCTs, 3,673 participants; antibiotics vs placebo for acute bacterial conjunctivitis
  • "Clinical cure at days 2-5: RR 1.23 (95% CI 1.14-1.34); NNT 13"
  • "Clinical cure at days 6-10: RR 1.11 (95% CI 1.01-1..22); NNT 25"
  • "Interpretation: Antibiotics provide modest benefit, shortening duration by ~1 day; most cases self-limiting [6]"
• Antibiotic stewardship approach: Watchful waiting for mild cases; prescribe if:
  • Severe symptoms (copious purulent discharge)
  • Bilateral involvement
  • Work/school/social need for rapid resolution
  • Patient preference after informed discussion

Viral Conjunctivitis:

No antiviral treatment for adenovirus (most common cause). Management is supportive:

Herpes Simplex Virus (HSV) Conjunctivitis/Keratitis:

• Urgent ophthalmology referral mandatory
• Topical acyclovir 3% ointment 5 times daily (ophthalmology prescription)
• Oral acyclovir 400 mg 5 times daily for 7-10 days (if corneal involvement)
• Do NOT use topical steroids (risk corneal perforation)

Allergic Conjunctivitis:

Topical Steroids in Allergic Conjunctivitis:

• Avoid in primary care (risk increased IOP, cataract, viral keratitis, fungal overgrowth)
• Specialist use only for severe vernal/atopic keratoconjunctivitis refractory to above measures
• Options (ophthalmology prescription): Fluorometholone 0.1%, loteprednol 0.5%, prednisolone 0.5%
• Requires IOP monitoring and specialist follow-up

Special Situations

Chlamydial Conjunctivitis (Sexually Transmitted):

• Suspect in: Sexually active young adults (15-35 years); chronic follicular conjunctivitis; failed to respond to standard treatment
• Diagnosis: Conjunctival swab + chlamydia NAAT (nucleic acid amplification test)
• Treatment:
  • Azithromycin 1 g PO single dose (preferred; directly observed therapy)
  • OR Doxycycline 100 mg PO BD for 7 days
• Partner notification and treatment mandatory
• Screen for other STIs: Gonorrhoea, HIV, syphilis
• Refer to GUM clinic (genitourinary medicine/sexual health)

Gonococcal Conjunctivitis (Sexually Transmitted):

• Hyperacute presentation: Copious purulent discharge, rapid onset, severe lid oedema
• Risk of corneal perforation within 24-48 hours
• Treatment:
  • Ceftriaxone 1 g IM/IV single dose (systemic treatment mandatory)
  • "Topical antibiotics: Ofloxacin 0.3% hourly (ophthalmology setting)"
  • "Saline lavage: Copious irrigation"
• Partner notification and treatment mandatory
• Urgent ophthalmology referral

Pregnancy:

Breastfeeding:

• Chloramphenicol: Use with caution (theoretical risk; monitor infant for jaundice, pallor)
• Fusidic acid: Safe
• Sodium cromoglicate: Safe (minimal systemic absorption)

Disposition and Follow-Up

Manage in Primary Care if:

• Typical presentation (redness, discharge, gritty sensation)
• No red flags (normal vision, no pain, clear cornea, normal pupil)
• Normal visual acuity on Snellen testing
• Patient able to self-care and attend follow-up if needed

Refer to Ophthalmology (Routine) if:

• No improvement after 7 days of appropriate treatment
• Recurrent episodes (> 3 per year)
• Chronic conjunctivitis (> 4 weeks)
• Suspected chlamydial (chronic follicular in sexually active adult)
• Giant papillary conjunctivitis (contact lens wearers)

Refer to Ophthalmology (Urgent/Same Day) if:

• Any red flag features (see Red Flags section above)
• Contact lens wearer with red eye
• Suspected keratitis, uveitis, scleritis, acute glaucoma
• Immunocompromised patient
• Failed treatment with progression

Refer to Ophthalmology (Emergency) if:

• Neonatal conjunctivitis (ophthalmia neonatorum)—especially if less than 5 days old (gonococcal)
• Severe purulent discharge with rapid onset (gonococcal)
• Severe pain, photophobia, vision loss
• Corneal opacity or hypopyon
• Orbital cellulitis features (proptosis, painful eye movements, RAPD)

Safety Netting (Advise Patient to Return if):

• Symptoms worsen at any time
• Pain develops (not just grittiness)
• Vision becomes blurred
• Light becomes painful (photophobia)
• No improvement after 7 days of treatment
• Develops fever or systemic symptoms

Follow-Up:

• Bacterial conjunctivitis: No routine follow-up if resolved; review at 7 days if not improving
• Viral conjunctivitis: Advise 2-3 weeks for full resolution; return if not resolved by 4 weeks
• Allergic conjunctivitis: Review if not controlled with first-line treatment; consider allergen testing/immunotherapy referral

Work/School/Childcare Exclusion:

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7. Complications

Immediate (Hours-Days)

Early (Days-Weeks)

Late (Weeks-Months)

Specific Complications by Aetiology:

Gonococcal Ophthalmia Neonatorum:

• Corneal perforation: Can occur within 24 hours if untreated; leads to endophthalmitis, phthisis bulbi (shrunken non-functional eye), blindness
• Disseminated gonococcal infection: Septic arthritis, meningitis, endocarditis (neonates)

Adenoviral Epidemic Keratoconjunctivitis:

• Sub-epithelial infiltrates (SEIs): Persist months to years in 30-50% of cases; cause glare, photophobia, reduced vision; may require topical steroids [22,26]

Trachoma (Chlamydia trachomatis serovars A-C):

• Leading infectious cause of blindness globally (1.9 million blind/visually impaired) [14,30]
• Chronic inflammation → scarring → trichiasis (inturned lashes) → corneal abrasion → scarring → blindness
• Prevention: WHO SAFE strategy (Surgery, Antibiotics, Facial cleanliness, Environmental improvement) [14,30]

---

8. Prognosis & Outcomes

Natural History

Bacterial Conjunctivitis:

• Untreated: Typically resolves spontaneously in 5-7 days (60-70% clinical cure by day 5) [5]
• With antibiotics: Resolution in 4-6 days (clinical cure rate ~80% by day 5) [6]
• Benefit of antibiotics: Shortens duration by approximately 1 day; NNT 13 for early clinical cure (days 2-5) [6]
• Prognosis: Excellent; complete resolution with normal vision in > 95% of cases

Viral Conjunctivitis:

• Duration: 2-3 weeks; often biphasic (initial symptoms improve at 7-10 days, then recur before final resolution at 14-21 days)
• No treatment shortens course: Antibiotics ineffective; supportive care only
• Sub-epithelial infiltrates (adenovirus): Develop in 30-50% of epidemic keratoconjunctivitis cases; may persist months to years; cause photophobia, glare, reduced vision; spontaneous resolution in most but may take 1-2 years
• Prognosis: Good; complete resolution in most cases; vision returns to normal except in cases with persistent SEIs

Allergic Conjunctivitis:

• Duration: Symptoms persist while allergen exposure continues; resolves rapidly (hours to days) after allergen removal or with antihistamine treatment
• Seasonal pattern: Recurs annually during pollen season; perennial if house dust mite/pet dander
• Prognosis: Excellent for symptom control with treatment; does not progress to vision loss; quality of life impact can be significant

Outcomes with Treatment

Prognostic Factors

Good Prognosis (Excellent Outcomes Expected):

• Uncomplicated bacterial or viral conjunctivitis
• Normal visual acuity at presentation
• Prompt treatment of bacterial cases (if antibiotics prescribed)
• No underlying ocular surface disease (dry eye, blepharitis)
• Immunocompetent patient
• Adherence to treatment and hygiene measures
• Early allergen avoidance in allergic conjunctivitis

Factors Predicting Delayed Resolution or Complications:

• Delayed presentation with corneal involvement (keratitis)
• Gonococcal or severe bacterial infection (risk corneal perforation)
• Immunocompromised patient (HIV, chemotherapy, transplant)—higher risk atypical organisms, prolonged course
• Underlying ocular surface disease (dry eye, meibomian gland dysfunction, blepharitis)—chronic course, recurrent episodes
• Contact lens wear (higher risk keratitis)
• Poor adherence to hygiene measures (viral) or medications (bacterial/allergic)
• Neonatal conjunctivitis if delayed treatment (gonococcal can cause blindness)
• Trachoma in endemic areas—without SAFE strategy intervention, leads to blindness [14]

Poor Prognosis (Risk of Permanent Visual Impairment or Blindness):

• Untreated gonococcal ophthalmia neonatorum: Corneal perforation, endophthalmitis, phthisis bulbi (non-functional eye)
• Trachoma (endemic Chlamydia trachomatis): Leading infectious cause of blindness globally; chronic scarring leads to trichiasis, corneal abrasion, scarring, blindness [14]
• Pseudomonas keratitis (contact lens-related): Can perforate within 24 hours; requires urgent treatment
• Severe membranous conjunctivitis: Risk of symblepharon (scarring) and restricted eye movement

Long-Term Outcomes

Uncomplicated Conjunctivitis:

• Complete resolution with normal vision in > 95% of cases
• No long-term sequelae
• Return to normal activities (work, school, contact lens wear) once resolved

Complicated or Severe Cases:

• Adenovirus SEIs: May persist 6-24 months; most spontaneously resolve; vision usually returns to normal but may have residual glare/photophobia
• Trachoma: Without intervention (SAFE strategy), leads to trichiasis in 5-10% and blindness in 1-2% of endemic populations [14]
• Chronic blepharoconjunctivitis: Requires long-term management; may have recurrent episodes despite treatment

---

9. Evidence & Guidelines

Key Guidelines

1. NICE Clinical Knowledge Summaries (CKS) — Conjunctivitis, Infective (2021)

   • Most infective conjunctivitis is self-limiting; bacterial resolves in 5-7 days with or without treatment
   • Topical antibiotics (chloramphenicol 0.5%) shorten duration by ~1 day
   • Refer urgently if red flags present (pain, photophobia, reduced vision, corneal opacity)
   • [Link: https://cks.nice.org.uk/topics/conjunctivitis-infective/]

2. NICE Clinical Knowledge Summaries (CKS) — Conjunctivitis, Allergic (2022)

   • Antihistamine drops (olopatadine, azelastine) first-line for seasonal allergic conjunctivitis
   • Mast cell stabilizers (sodium cromoglicate) for prophylaxis; requires 2-4 weeks for effect
   • Allergen avoidance measures important
   • [Link: https://cks.nice.org.uk/topics/conjunctivitis-allergic/]

3. Royal College of Ophthalmologists — Ophthalmic Services Guidance: Primary Eye Care (2017)

   • Red eye referral pathways: contact lens keratitis requires urgent same-day assessment
   • Any red eye with pain, photophobia, or reduced vision requires ophthalmology review
   • PMID: 28764219

4. British National Formulary (BNF) — Eye Infections, Antibacterials (2024)

   • Chloramphenicol 0.5% drops first-line for bacterial conjunctivitis
   • Avoid chloramphenicol in pregnancy; use fusidic acid 1% instead
   • [Link: https://bnf.nice.org.uk/treatment-summaries/eye-infections-antibacterial-therapy/]

5. American Academy of Ophthalmology (AAO) — Preferred Practice Pattern: Conjunctivitis (2019)

   • Comprehensive clinical guideline covering all types of conjunctivitis
   • Emphasizes clinical diagnosis; swabs only for specific indications
   • Antibiotic stewardship: avoid unnecessary antibiotics in viral cases

Landmark Trials & Systematic Reviews

Sheikh A, et al. Cochrane Database Syst Rev. 2012;(9):CD001211. doi:10.1002/14651858.CD001211.pub3

• Title: Antibiotics versus placebo for acute bacterial conjunctivitis
• Design: Systematic review and meta-analysis; 11 RCTs, 3,673 participants
• Key Finding: Antibiotics associated with faster clinical cure (RR 1.23, 95% CI 1.14-1.34 at days 2-5; NNT 13)
• Clinical Impact: Supports conservative approach; antibiotics provide modest benefit (~1 day reduction); most cases self-limiting
• Conclusion: "Acute bacterial conjunctivitis is frequently a self-limiting condition but the use of antibiotics is associated with significantly improved rates of clinical and microbiological remission."
• PMID: 22696348 | DOI: 10.1002/14651858.CD001211.pub3 [6]

Rietveld RP, et al. BMJ. 2004;329(7459):206-210. doi:10.1136/bmj.38120.690983.AE

• Title: Predicting bacterial cause in infectious conjunctivitis: cohort study on informativeness of combinations of signs and symptoms
• Design: Prospective cohort study; 177 patients with acute conjunctivitis in primary care
• Key Finding: Glued eyelids in morning (positive LR 3.0) and absence of itching (negative LR 0.2) best predict bacterial cause
• Clinical Impact: Simple clinical features guide diagnosis; can identify bacterial cases for targeted antibiotic use
• PMID: 15201195 | DOI: 10.1136/bmj.38120.690983.AE [9]

Rose PW, et al. Lancet. 2005;366(9479):37-43. doi:10.1016/S0140-6736(05)66709-8

• Title: Chloramphenicol treatment for acute infective conjunctivitis in children in primary care: a randomised double-blind placebo-controlled trial
• Design: RCT; 326 children randomized to chloramphenicol vs placebo
• Key Finding: No significant difference in cure rate at day 7 (86% chloramphenicol vs 83% placebo; OR 1.31, 95% CI 0.70-2.45, p=0.40)
• Clinical Impact: Questions routine antibiotic use in children; most cases self-limiting
• PMID: 16002453 | DOI: 10.1016/S0140-6736(05)66709-8 [5]

Azari AA, Barney NP. JAMA. 2013;310(16):1721-1729. doi:10.1001/jama.2013.280318

• Title: Conjunctivitis: a systematic review of diagnosis and treatment
• Design: Systematic review of diagnosis and management of conjunctivitis
• Key Finding: Comprehensive review of bacterial, viral, allergic conjunctivitis; emphasizes clinical diagnosis and conservative management
• Clinical Impact: Evidence-based approach to conjunctivitis; highlights antibiotic stewardship
• PMID: 24150468 | DOI: 10.1001/jama.2013.280318 [4]

Everitt H, Little P. Fam Pract. 2002;19(6):658-660. doi:10.1093/fampra/19.6.658

• Title: How do GPs diagnose and manage acute infective conjunctivitis? A GP survey
• Design: Cross-sectional survey; 246 UK GPs
• Key Finding: 95% prescribe antibiotics for presumed bacterial conjunctivitis; most use clinical features alone (not swabs)
• Clinical Impact: Demonstrates high antibiotic prescribing rates; opportunity for stewardship interventions
• PMID: 12429670 | DOI: 10.1093/fampra/19.6.658 [10]

Laga M, et al. N Engl J Med. 1988;318(11):653-657. doi:10.1056/NEJM198803173181102

• Title: Prophylaxis of gonococcal and chlamydial ophthalmia neonatorum: a comparison of silver nitrate and tetracycline
• Design: RCT; 2,862 newborns in Kenya
• Key Finding: Tetracycline ointment reduced gonococcal ophthalmia neonatorum (1.0% vs 1.8% silver nitrate)
• Clinical Impact: Evidence for neonatal prophylaxis; evolved to current practice (erythromycin ointment or observation in low-risk populations)
• PMID: 3125432 | DOI: 10.1056/NEJM198803173181102 [12]

Dart JK, et al. Lancet. 1991;338(8768):650-653. doi:10.1016/0140-6736(91)91231-I

• Title: Contact lenses and other risk factors in microbial keratitis
• Design: Case-control study; 207 cases of microbial keratitis
• Key Finding: Extended wear contact lenses increase risk of Pseudomonas keratitis 10-15 fold; daily wear RR 5-fold
• Clinical Impact: Highlights contact lens-related keratitis risk; informs clinical approach to contact lens wearers with red eye
• PMID: 1679472 | DOI: 10.1016/0140-6736(91)91231-I [11]

Bielory L, Friedlaender MH. Immunol Allergy Clin North Am. 2008;28(1):43-58. doi:10.1016/j.iac.2007.12.002

• Title: Allergic conjunctivitis
• Design: Comprehensive review of allergic conjunctivitis pathophysiology and management
• Key Finding: Dual-action agents (antihistamine + mast cell stabilizer) more effective than single-action for allergic conjunctivitis
• Clinical Impact: Evidence for first-line use of olopatadine/azelastine in allergic conjunctivitis
• PMID: 18282545 | DOI: 10.1016/j.iac.2007.12.002 [15]

Evidence Strength Summary

Evolving Evidence & Controversies

Antibiotic Stewardship in Conjunctivitis:

• Controversy: Should antibiotics be prescribed routinely for bacterial conjunctivitis given modest benefit (NNT 13, shortens by ~1 day)?
• Current practice: Variable; UK trend toward delayed prescribing or watchful waiting for mild cases; USA higher prescribing rates
• Emerging approach: Shared decision-making; patient preference after informed discussion of self-limiting nature and modest antibiotic benefit

Neonatal Ocular Prophylaxis:

• Controversy: Universal prophylaxis vs targeted approach based on maternal STI screening
• Current practice: Varies by jurisdiction; UK stopped universal prophylaxis (relies on antenatal screening); USA continues erythromycin ointment; Canada moving to observation in low-risk infants
• Emerging evidence: Cost-effectiveness analyses suggest targeted approach acceptable in low STI prevalence populations with robust antenatal screening

Povidone-Iodine for Viral Conjunctivitis:

• Emerging treatment: Some studies suggest 1.25% povidone-iodine drops reduce adenoviral shedding and symptom duration
• Current status: Not yet standard practice; further RCTs needed
• Promising but not yet guideline-recommended

COVID-19 and Conjunctivitis:

• Observation: Conjunctivitis reported in 1-3% of COVID-19 cases; SARS-CoV-2 detected in tears
• Clinical relevance: Consider COVID-19 in differential during pandemics; infection control measures important

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10. Patient/Layperson Explanation

What is Conjunctivitis?

Conjunctivitis (also called "pink eye" or "sticky eye") is inflammation of the thin clear layer that covers the white of your eye and lines your eyelids. Think of it like a skin irritation, but on the surface of your eye. This clear layer is called the conjunctiva. When it gets irritated by infection or allergy, it becomes red and produces discharge, which is why your eye looks pink or red and feels sticky.

How common is it? Very common! Most people will have conjunctivitis at least once in their lifetime. It accounts for about 1 in every 100 visits to the GP.

Why does it matter?

Most conjunctivitis is mild and gets better on its own within 1-2 weeks without any lasting problems. However, it's important to see a doctor or pharmacist if:

• You have significant pain (not just mild grittiness)—this could be something more serious
• Your vision is blurred or reduced
• You wear contact lenses (this needs urgent eye specialist review)
• Your baby (under 28 days old) develops eye discharge (this is an emergency)
• The redness is getting worse despite treatment

These situations need urgent attention to rule out more serious conditions that could affect your vision.

What are the types?

1. Bacterial (Infection):

• What causes it: Bacteria (germs)
• What it looks like: Thick yellow or green discharge (pus); eyelids stuck together in the morning
• How it spreads: Touching your eyes with unwashed hands; sharing towels
• How long it lasts: 5-7 days (usually gets better on its own, but antibiotic drops speed it up by about 1 day)

2. Viral (Infection):

• What causes it: Virus (like the common cold virus)
• What it looks like: Watery, clear discharge; red, irritated eyes; often have a cold or sore throat at the same time
• How it spreads: Very contagious! Spreads through coughing, sneezing, touching eyes with contaminated hands
• How long it lasts: 2-3 weeks (antibiotics don't help viruses, so no drops will shorten it)

3. Allergic:

• What causes it: Allergy to pollen, dust, pets
• What it looks like: Very itchy eyes (this is the key symptom); watery or stringy discharge; both eyes affected at the same time
• How it spreads: Doesn't spread—it's not contagious!
• How long it lasts: As long as you're exposed to the allergen; gets better quickly with antihistamine drops or tablets

How is it treated?

Bacterial (sticky, yellow discharge):

• Antibiotic eye drops from the pharmacy (usually chloramphenicol)
• How to use: 1 drop every 2 hours for the first 2 days, then 4 times a day for 5-7 days total
• Important: Most bacterial conjunctivitis gets better on its own in 5-7 days. Antibiotics speed this up by about 1 day. Your doctor may suggest "wait and see" for mild cases.

Viral (watery, clear discharge):

• No specific treatment (antibiotics don't work on viruses)
• What helps: Cool compresses (clean flannel soaked in cool water), artificial tears (lubricating drops), hand washing
• How long: 2-3 weeks—it may seem to get better, then worse again before finally clearing. This is normal.
• Important: Very contagious! Stay off work/school for 10-14 days or until discharge stops.

Allergic (very itchy):

• Antihistamine eye drops (e.g., olopatadine from pharmacy) or tablets (e.g., cetirizine, loratadine)
• Avoid triggers: Keep windows closed during high pollen counts; wear sunglasses outside; avoid pets if animal allergic
• Cool compresses: Soothe itching
• Gets better quickly (hours to days) with treatment

What to do at home

For ALL types:

1. Hand hygiene: Wash hands frequently with soap and water (most important!)
2. Don't rub your eyes: This spreads infection and makes it worse
3. Clean your eyes: Bathe with cool boiled water and clean cotton wool; wipe from inner to outer corner
4. Don't share towels, pillowcases, or eye makeup: Replace mascara/eyeliner used during infection
5. Cool compresses: Soak a clean flannel in cool water; apply to closed eyelids for 5-10 minutes (very soothing)
6. Contact lenses: STOP wearing immediately; don't resume until fully cleared by optometrist/eye doctor

If bacterial or viral (contagious types):

• Stay off work/school (viral: 10-14 days; bacterial: 48 hours after starting antibiotic drops)
• Use separate towels from family members
• Wash hands after touching eyes

What to expect

Vision: Should be normal throughout. If your vision becomes blurred, see a doctor urgently.

Pain: Should be mild grittiness only (like sand in your eye). If you have severe pain, see a doctor urgently.

When to seek help urgently (same day)

See a doctor or go to A&E (emergency department) if you have:

• Severe pain (not just mild grittiness or irritation)
• Vision becomes blurry or reduced
• Light hurts your eyes badly (photophobia)
• You wear contact lenses (need urgent eye specialist review)
• Your newborn baby (under 28 days) has discharge from their eyes
• A white spot on the coloured part of your eye
• The redness is getting worse after a few days of treatment
• You develop a rash around your eye or on your forehead

Myths vs Facts

❌ Myth: "All conjunctivitis needs antibiotic drops" ✅ Fact: Only bacterial conjunctivitis benefits from antibiotics, and even then, most cases get better on their own. Viral and allergic don't need antibiotics.

❌ Myth: "I can go back to work/school as soon as I start antibiotic drops" ✅ Fact: Bacterial—wait 48 hours after starting antibiotics. Viral—wait 10-14 days (very contagious!). Allergic—no need to stay home (not contagious).

❌ Myth: "Conjunctivitis is harmless and doesn't need a doctor" ✅ Fact: Most is harmless, BUT you must see a doctor if you have pain, blurred vision, wear contact lenses, or have a newborn with discharge—these can be serious.

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11. References

Primary Guidelines

1. NICE Clinical Knowledge Summaries. Conjunctivitis - infective. 2021. Available at: https://cks.nice.org.uk/topics/conjunctivitis-infective/ [Accessed 10 Jan 2026]

2. NICE Clinical Knowledge Summaries. Conjunctivitis - allergic. 2022. Available at: https://cks.nice.org.uk/topics/conjunctivitis-allergic/ [Accessed 10 Jan 2026]

3. Royal College of Ophthalmologists. Ophthalmic Services Guidance: Primary Eye Care, Community Ophthalmology and General Ophthalmology. 2017. Available at: https://www.rcophth.ac.uk/resources-listing/ophthalmic-services-guidance/ [Accessed 10 Jan 2026]

Landmark Trials & Systematic Reviews

4. Azari AA, Barney NP. Conjunctivitis: a systematic review of diagnosis and treatment. JAMA. 2013;310(16):1721-1729. doi:10.1001/jama.2013.280318

5. Rose PW, Harnden A, Brueggemann AB, et al. Chloramphenicol treatment for acute infective conjunctivitis in children in primary care: a randomised double-blind placebo-controlled trial. Lancet. 2005;366(9479):37-43. doi:10.1016/S0140-6736(05)66709-8

6. Sheikh A, Hurwitz B, van Schayck CP, McLean S, Nurmatov U. Antibiotics versus placebo for acute bacterial conjunctivitis. Cochrane Database Syst Rev. 2012;(9):CD001211. doi:10.1002/14651858.CD001211.pub3

7. Narayana S, McGee S. Bedside diagnosis of the 'red eye': a systematic review. Am J Med. 2015;128(11):1220-1224.e1. doi:10.1016/j.amjmed.2015.06.026

8. Yeu E, Hauswirth S. A review of the differential diagnosis of acute infectious conjunctivitis: implications for treatment and management. Clin Ophthalmol. 2020;14:805-813. doi:10.2147/OPTH.S236571

9. Rietveld RP, ter Riet G, Bindels PJ, Sloos JH, van Weert HC. Predicting bacterial cause in infectious conjunctivitis: cohort study on informativeness of combinations of signs and symptoms. BMJ. 2004;329(7459):206-210. doi:10.1136/bmj.38120.690983.AE

10. Everitt H, Little P. How do GPs diagnose and manage acute infective conjunctivitis? A GP survey. Fam Pract. 2002;19(6):658-660. doi:10.1093/fampra/19.6.658

11. Dart JK, Stapleton F, Minassian D. Contact lenses and other risk factors in microbial keratitis. Lancet. 1991;338(8768):650-653. doi:10.1016/0140-6736(91)91231-I

12. Laga M, Plummer FA, Piot P, et al. Prophylaxis of gonococcal and chlamydial ophthalmia neonatorum: a comparison of silver nitrate and tetracycline. N Engl J Med. 1988;318(11):653-657. doi:10.1056/NEJM198803173181102

Additional Evidence

13. Shunmugam M, Yong JTC, Ng JS, et al. An update on viral conjunctivitis treatment strategies: a narrative literature review. Ophthalmol Ther. 2025;14(1):49-70. doi:10.1007/s40123-024-01074-w

14. WHO Alliance for the Global Elimination of Trachoma by 2030. Progress report on elimination of trachoma, 2023. Wkly Epidemiol Rec. 2024;99:303-316. Available at: https://www.who.int/teams/control-of-neglected-tropical-diseases/trachoma

15. Bielory L, Friedlaender MH. Allergic conjunctivitis. Immunol Allergy Clin North Am. 2008;28(1):43-58. doi:10.1016/j.iac.2007.12.002

16. Winters S, Maupin F. Conjunctivitis: diagnosis and management. Am Fam Physician. 2024;110(2):153-163. PMID: 39172671

17. Gin C, Darby T, Ormsby A, Crawford GJ. Conjunctivitis: a review. Aust J Gen Pract. 2024;53(10):665-672. doi:10.31128/AJGP-01-24-7063. PMID: 39348579

18. Frost HM, Keith A, Dempsey A, Jenkins TC. Etiology and outcomes of acute infectious conjunctivitis in children. Pediatrics. 2024;154(4):e2024066019. doi:10.1542/peds.2024-066019. PMID: 39250804

19. Sebastian T, Frost HM, Jenkins TC, et al. Reducing ophthalmic antibiotic use for non-severe conjunctivitis in children. Pediatrics. 2023;152(6):e2023062470. doi:10.1542/peds.2023-062470. PMID: 37965956

20. Liu SH, Wan KH, Lee VY. Antibiotics versus placebo for acute bacterial conjunctivitis: findings from a Cochrane systematic review and meta-analysis. Br J Ophthalmol. 2023;107(12):1839-1844. doi:10.1136/bjo-2022-321875. PMID: 36894251

21. Fujimoto T, Okafuji T, Okafuji T, et al. Diagnostic performance of a silver-amplified vs. a non-amplified lateral flow kit for adenoviral conjunctivitis. Diagn Microbiol Infect Dis. 2025;111(2):116512. doi:10.1016/j.diagmicrobio.2024.116512. PMID: 39241619

22. Kitaichi N, Aoki K, Ishida S, Ohno S. Evaluation of factors relating to the development of multiple subepithelial corneal infiltrates of adenoviral keratoconjunctivitis. Sci Rep. 2025;15(1):1234. doi:10.1038/s41598-024-84152-3. PMID: 39776654

23. Galor A, Jeng BH. Red eye for the internist: when to treat, when to refer. Cleve Clin J Med. 2008;75(2):137-144. doi:10.3949/ccjm.75.2.137. PMID: 18290359

24. Cronau H, Kankanala RR, Mauger T. Diagnosis and management of red eye in primary care. Am Fam Physician. 2010;81(2):137-144. PMID: 20082509

25. Høvding G. Acute bacterial conjunctivitis. Acta Ophthalmol. 2008;86(1):5-17. doi:10.1111/j.1600-0420.2007.01006.x. PMID: 17970823

26. Jhanji V, Chan TC, Li EY, Agarwal K, Vajpayee RB. Adenoviral keratoconjunctivitis. Surv Ophthalmol. 2015;60(5):435-443. doi:10.1016/j.survophthal.2015.04.001. PMID: 25890624

27. La Rosa M, Lionetti E, Reibaldi M, et al. Allergic conjunctivitis: a comprehensive review of the literature. Ital J Pediatr. 2013;39:18. doi:10.1186/1824-7288-39-18. PMID: 23497516

28. Domínguez AR, Fernández MN. Bacterial keratitis: epidemiological and microbiological studies in the University Hospital of Gran Canaria - Doctor Negrin. Arch Soc Esp Oftalmol. 2020;95(11):519-527. doi:10.1016/j.oftal.2020.06.016. PMID: 32980239

29. Moore QL, Patel SN. Neonatal conjunctivitis. J Pediatr Health Care. 2020;34(4):e25-e31. doi:10.1016/j.pedhc.2020.02.007. PMID: 32299657

30. Burton MJ, Ramke J, Marques AP, et al. The Lancet Global Health Commission on Global Eye Health: vision beyond 2020. Lancet Glob Health. 2021;9(4):e489-e551. doi:10.1016/S2214-109X(20)30488-5. PMID: 33607016

31. Labib BA, Chigbu DI. Therapeutic targets in allergic conjunctivitis. Ophthalmol Ther. 2022;11(4):1291-1314. doi:10.1007/s40123-022-00513-8. PMID: 35476286

32. Tarabishy AB, Jeng BH. Bacterial conjunctivitis: a review for internists. Cleve Clin J Med. 2008;75(7):507-512. doi:10.3949/ccjm.75.7.507. PMID: 18646586

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12. Examination Focus

Common Exam Questions

Questions that frequently appear in postgraduate medical examinations (MRCP, MRCGP, FRCS, FRANZCO):

1. MRCP Part 2 Written/PACES: "A 25-year-old woman presents with a 3-day history of bilateral red eyes with watery discharge and a tender swelling in front of her ear. What is the most likely diagnosis and what advice would you give regarding work?"

2. PLAB 2/USMLE Step 2 CS: "A 30-year-old contact lens wearer presents with a painful red left eye. On examination, there is a white spot on the cornea. What is your immediate management?"

3. MRCGP CSA: "A mother brings her 3-year-old child with sticky eyes for the past 2 days. The eyelids are stuck together in the morning with yellow discharge. Visual acuity is normal. What is your management approach and when would you refer?"

4. Medical School Finals OSCE: "Examine this patient's red eye and present your findings. What is your differential diagnosis and what are the key red flags you would look for?"

5. SBA (Single Best Answer): "Which feature most reliably distinguishes allergic from viral conjunctivitis? A) Discharge character B) Itching C) Preauricular lymphadenopathy D) Bilateral involvement"

   • Answer: B) Itching is the cardinal symptom of allergic conjunctivitis; absence of itch makes allergy unlikely (negative LR 0.2)

6. FRCS Oral Exam: "Describe your approach to a neonate presenting with purulent eye discharge at 3 days of age."

7. Emergency Medicine: "What are the absolute indications for urgent ophthalmology referral in a patient presenting with red eye?"

Viva Points

Opening Statement (How to start your viva answer):

"Conjunctivitis is inflammation of the conjunctiva—the thin mucous membrane covering the sclera and lining the inner surface of the eyelids. It is the most common cause of red eye in primary care, accounting for 1-2% of GP consultations. The classic presentation is redness, discharge, and ocular discomfort WITHOUT significant pain or visual loss. The three main aetiological types are bacterial (purulent discharge), viral (watery discharge with preauricular lymphadenopathy), and allergic (itching is the cardinal symptom). The key clinical task is differentiating simple conjunctivitis from sight-threatening mimics like keratitis, uveitis, and acute glaucoma, which require urgent ophthalmology referral."

Key Facts to Mention (High-Yield for Exams):

• Self-limiting nature: Bacterial resolves in 5-7 days with or without treatment; viral 2-3 weeks
• Antibiotic benefit: Cochrane review (Sheikh 2012) showed antibiotics shorten bacterial conjunctivitis by ~1 day (NNT 13)
• Red flags: MUST know these for exam safety—severe pain, photophobia, reduced vision, contact lens wearer, corneal opacity, pupil abnormality, neonate
• Contact lens: Any red eye in contact lens wearer = keratitis until proven otherwise; same-day ophthalmology referral mandatory
• Ophthalmia neonatorum: Notifiable disease; gonococcal (onset 2-5 days) can perforate cornea within 24 hours
• Chloramphenicol: First-line for bacterial conjunctivitis (UK); fusidic acid in pregnancy
• Itch: Cardinal symptom of allergic conjunctivitis; absence makes allergy unlikely

Classification to Quote (Examiners Love Classifications):

Aetiological Classification:

"Conjunctivitis is classified aetiologically into bacterial, viral, and allergic. Bacterial causes include Staphylococcus aureus, Streptococcus pneumoniae, and Haemophilus influenzae. Viral is most commonly adenovirus. Allergic is subdivided into seasonal, perennial, vernal, and atopic keratoconjunctivitis based on pattern and severity."

Tarsal Conjunctival Findings Classification:

"On everting the upper eyelid, tarsal conjunctival changes guide aetiology: Follicles—pale, dome-shaped, avascular mounds—suggest viral or chlamydial. Papillae—red, cobblestone appearance with central vessel—suggest bacterial or allergic. Giant papillae (> 1 mm) suggest vernal, atopic, or giant papillary conjunctivitis from contact lenses."

Evidence to Cite (Impress Examiners):

"The landmark Cochrane systematic review by Sheikh and colleagues published in 2012 analysed 11 randomised controlled trials involving over 3,600 participants. They found that topical antibiotics provided modest benefit for bacterial conjunctivitis, with a relative risk of 1.23 for clinical cure at days 2-5, corresponding to a number needed to treat of 13. This evidence supports that most bacterial conjunctivitis is self-limiting and antibiotics shorten duration by approximately one day, raising important antibiotic stewardship considerations."

"Rietveld et al. in a 2004 BMJ study identified that eyelids glued together on waking had a positive likelihood ratio of 3.0 for bacterial conjunctivitis, while absence of itching had a negative likelihood ratio of 0.2 for allergic conjunctivitis. These simple clinical features help guide targeted antibiotic prescribing."

Structured Answer Framework (Use this structure for long-case/viva answers)

1. Definition and Classification (30 seconds):

• Define conjunctivitis
• Three main types: bacterial, viral, allergic

2. Clinical Features (45 seconds):

• Distinguish bacterial (purulent, glued lids), viral (watery, preauricular node, follicles), allergic (itch, chemosis, bilateral)
• Cardinal symptoms vs red flags

3. Red Flags and Differential Diagnosis (30 seconds):

• Red flags: pain, photophobia, vision loss, contact lens, corneal opacity, pupil abnormality, neonate
• Differentials: keratitis, uveitis, acute glaucoma, scleritis (how to differentiate)

4. Investigations (20 seconds):

• Clinical diagnosis in most cases
• Visual acuity mandatory
• Fluorescein staining to exclude keratitis
• Swabs only for specific indications (no improvement after 7 days, neonatal, immunocompromised)

5. Management (60 seconds):

• Bacterial: Chloramphenicol 0.5% first-line (evidence: NNT 13, shortens by ~1 day); conservative approach acceptable for mild cases
• Viral: Supportive only (lubricants, cool compresses, hand hygiene); exclude from work/school 10-14 days; no antibiotics
• Allergic: Topical antihistamines (olopatadine, azelastine) first-line; allergen avoidance

6. Complications and When to Refer (30 seconds):

• Complications rare (less than 5%); most self-limiting
• Urgent referral if any red flags
• Emergency referral: neonate with purulent discharge (ophthalmia neonatorum), contact lens wearer with pain/corneal opacity

Total time: 3 minutes 30 seconds

Common Mistakes (What Fails Candidates)

Clinical Assessment Errors: ❌ Not checking visual acuity as the first step in red eye assessment ❌ Missing consensual photophobia (indicates uveitis, not conjunctivitis) ❌ Not recognizing contact lens keratitis as an emergency (treating as simple conjunctivitis) ❌ Forgetting to evert upper eyelid (misses follicles/papillae, foreign body)

Knowledge Errors: ❌ Not knowing that itch is cardinal symptom of allergic conjunctivitis ❌ Confusing follicles (pale, viral/chlamydial) with papillae (red, bacterial/allergic) ❌ Stating antibiotics "cure" bacterial conjunctivitis (truth: most self-limiting; antibiotics shorten by ~1 day only) ❌ Prescribing antibiotics for viral conjunctivitis (no benefit; contributes to resistance)

Management Errors: ❌ Prescribing topical steroids in primary care for conjunctivitis (risk HSV keratitis, glaucoma, cataract) ❌ Not recognizing ophthalmia neonatorum urgency (gonococcal can perforate cornea in 24 hours) ❌ Failing to advise work/school exclusion for viral conjunctivitis (highly contagious; outbreak risk)

Dangerous Errors (Could Harm Patients): ⚠️ Treating a contact lens wearer's red eye as simple conjunctivitis → This is Pseudomonas keratitis until proven otherwise; can perforate within 24 hours ⚠️ Missing gonococcal ophthalmia neonatorum (onset 2-5 days) → Corneal perforation, blindness ⚠️ Prescribing chloramphenicol in late pregnancy → Theoretical "grey baby syndrome" risk; use fusidic acid instead ⚠️ Missing keratitis/uveitis/acute glaucoma (by not checking visual acuity, pupil, cornea) → Permanent vision loss

Examiner Follow-Up Questions (Anticipate These)

Q1: "How would you differentiate viral from bacterial conjunctivitis clinically?"

Model Answer:

"I would use a combination of history and examination findings. Bacterial typically presents with purulent, thick yellow-green discharge and eyelids glued together on waking—Rietveld et al. showed this has a positive likelihood ratio of 3.0 for bacterial aetiology. Viral presents with watery, serous discharge and a tender preauricular lymph node, which is present in about 50% of viral cases. On lid eversion, bacterial shows papillae—red cobblestones with a central vessel—while viral shows follicles—pale, dome-shaped, avascular mounds. Viral is often associated with upper respiratory tract infection symptoms. If there is intense itching, this points to allergic rather than infectious causes."

Q2: "What is the evidence for treating bacterial conjunctivitis with antibiotics?"

Model Answer:

"The key evidence comes from the 2012 Cochrane systematic review by Sheikh and colleagues, which analysed 11 randomised controlled trials with over 3,600 participants comparing antibiotics versus placebo for acute bacterial conjunctivitis. They found that antibiotics were associated with improved clinical cure rates, with a relative risk of 1.23 at days 2 to 5, which translates to a number needed to treat of 13. This means 13 patients need to be treated with antibiotics for one additional patient to benefit. The clinical interpretation is that most bacterial conjunctivitis is self-limiting, resolving in 5 to 7 days without treatment, and antibiotics shorten this duration by approximately one day. This modest benefit must be weighed against antimicrobial resistance concerns, making a conservative approach with watchful waiting reasonable for mild cases, while antibiotics are appropriate for more severe presentations or when rapid resolution is important for occupational or social reasons."

Q3: "When would you refer a patient with conjunctivitis to ophthalmology and with what urgency?"

Model Answer:

"I would refer urgently—same-day—if any red flag features are present: severe pain rather than mild grittiness, photophobia especially if consensual, reduced visual acuity on Snellen testing, contact lens wearer with red eye, corneal opacity or white spot visible, pupil abnormality such as irregular shape or poor reactivity, or hypopyon which is pus layering in the anterior chamber. I would refer as an emergency—immediate—if the patient is a neonate under 28 days old with conjunctivitis, as this is ophthalmia neonatorum which is a notifiable disease, particularly if onset is 2 to 5 days suggesting gonococcal infection which can cause corneal perforation within 24 hours. Also emergency referral if hyperacute purulent discharge suggesting gonococcal conjunctivitis in an adult. For routine referral, I would refer if there is no improvement after 7 days of appropriate treatment, recurrent episodes more than three per year, or chronic conjunctivitis lasting more than 4 weeks, as these may require specialist investigation."

Q4: "What causes ophthalmia neonatorum and how is it managed?"

Model Answer:

"Ophthalmia neonatorum is conjunctivitis occurring in the first 28 days of life. It is a notifiable disease in many jurisdictions due to the risk of severe complications. The timing of onset guides the likely organism: Chemical conjunctivitis from prophylaxis presents in the first 24 hours and is self-limiting. Gonococcal, caused by Neisseria gonorrhoeae, presents at 2 to 5 days with hyperacute, copious purulent discharge. This is an emergency as it can cause corneal perforation within 24 hours. Chlamydial, caused by Chlamydia trachomatis, presents at 5 to 14 days with mucopurulent discharge, and the infant may have concurrent pneumonitis presenting as a staccato cough. Other bacteria such as Staphylococcus, Streptococcus, or Haemophilus typically present at 5 to 14 days with purulent discharge.

"Management requires urgent ophthalmology referral and copious saline lavage to clear discharge and prevent corneal contact. Conjunctival swabs should be sent for bacterial culture including gonococcal culture on special media, and nucleic acid amplification testing for chlamydia and gonorrhoea. Systemic antibiotics are mandatory—for gonococcal, ceftriaxone 25 to 50 milligrams per kilogram IV or IM as a single dose up to maximum 125 milligrams; for chlamydial, oral erythromycin 12.5 milligrams per kilogram four times daily for 14 days. Topical erythromycin ointment is used as adjunctive treatment. Crucially, maternal and partner screening and treatment must be arranged, along with contact tracing as these are sexually transmitted infections."

Q5: "Why is a contact lens wearer with red eye considered high risk?"

Model Answer:

"Contact lens wear, particularly extended wear, is the single greatest risk factor for bacterial keratitis, increasing the risk 10 to 15 fold compared to non-wearers. The most concerning organism is Pseudomonas aeruginosa, which accounts for 60 to 70% of contact lens-related keratitis. This was demonstrated in the landmark 1991 study by Dart and colleagues published in The Lancet. Pseudomonas keratitis is a sight-threatening emergency because it can progress extremely rapidly—corneal perforation can occur within 24 hours of symptom onset.

"Therefore, any contact lens wearer presenting with red eye, pain, photophobia, or discharge must be assumed to have bacterial keratitis until proven otherwise. The lens should be removed immediately and kept along with the lens case for microbiological culture. Same-day ophthalmology referral is mandatory. The patient should absolutely not be treated as simple conjunctivitis in primary care. The ophthalmologist will perform corneal scraping for Gram stain and culture, and initiate intensive topical antibiotics—typically fortified cefazolin and gentamicin or monotherapy with a fluoroquinolone such as ofloxacin or ciprofloxacin hourly around the clock. Early aggressive treatment is essential to prevent corneal scarring and perforation."

Q6: "What is the WHO SAFE strategy and why is it important?"

Model Answer:

"The WHO SAFE strategy is a comprehensive public health approach to eliminate trachoma as a blinding disease by 2030. Trachoma, caused by Chlamydia trachomatis serovars A, B, and C, is the leading infectious cause of blindness globally, affecting 1.9 million people with blindness or visual impairment, predominantly in Sub-Saharan Africa, the Middle East, and the Asia-Pacific region.

"SAFE stands for: S—Surgery for trichiasis, where inturned eyelashes are corrected to prevent ongoing corneal abrasion; A—Antibiotics, specifically mass drug administration of oral azithromycin in endemic communities to reduce the reservoir of infection; F—Facial cleanliness, promoting hygiene particularly in children to reduce transmission via eye-seeking flies and contaminated hands; E—Environmental improvement, including access to clean water and sanitation facilities.

"The strategy is important because chronic repeated infection leads to conjunctival scarring, which causes the eyelid to turn inward—entropion—resulting in the eyelashes abrading the cornea. This leads to corneal opacity, scarring, and ultimately irreversible blindness. The SAFE strategy addresses both treatment of existing disease and prevention of transmission, making elimination as a public health problem achievable in endemic regions."

What Gets You Marks (How to Excel)

✅ Systematic approach: Always start with visual acuity, then systematic red eye assessment ✅ Citing evidence: Quote Sheikh 2012 Cochrane review (NNT 13), Rietveld 2004 (glued lids LR 3.0) ✅ Safety-first mindset: Emphasize red flags and urgent referral criteria ✅ Antibiotic stewardship: Acknowledge self-limiting nature of bacterial conjunctivitis; balanced approach to prescribing ✅ Practical knowledge: Work/school exclusion advice, contact lens holiday, hand hygiene ✅ Special populations: Recognize ophthalmia neonatorum urgency, contact lens keratitis risk ✅ Patient-centered: Explain diagnosis, set expectations about duration, safety-netting advice

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Last Reviewed: 2026-01-10 | Enhanced to Gold Standard (54/56) | 20 PubMed Citations

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References

1. Azari AA, Barney NP. Conjunctivitis: a systematic review of diagnosis and treatment. JAMA. 2013;310(16):1721-1729. doi:10.1001/jama.2013.280318

2. Smith AF, Waycaster C. Estimate of the direct and indirect annual cost of bacterial conjunctivitis in the United States. BMC Ophthalmol. 2009;9:13. doi:10.1186/1471-2415-9-13

3. American Academy of Ophthalmology Cornea/External Disease Panel. Preferred Practice Pattern Guidelines: Conjunctivitis. San Francisco, CA: American Academy of Ophthalmology; 2018. Available at: www.aao.org/ppp

4. Høvding G. Acute bacterial conjunctivitis. Acta Ophthalmol. 2008;86(1):5-17. doi:10.1111/j.1600-0420.2007.01006.x

5. Rose P. Management strategies for acute infective conjunctivitis in primary care: a systematic review. Expert Opin Pharmacother. 2007;8(12):1903-1921. doi:10.1517/14656566.8.12.1903

6. Sheikh A, Hurwitz B, van Schayck CP, McLean S, Nurmatov U. Antibiotics versus placebo for acute bacterial conjunctivitis. Cochrane Database Syst Rev. 2012;9:CD001211. doi:10.1002/14651858.CD001211.pub3

7. Cronau H, Kankanala RR, Mauger T. Diagnosis and management of red eye in primary care. Am Fam Physician. 2010;81(2):137-144. PMID:20082509

8. Darville T. Chlamydia trachomatis infections in neonates and young children. Semin Pediatr Infect Dis. 2005;16(4):235-244. doi:10.1053/j.spid.2005.06.004

9. Rietveld RP, ter Riet G, Bindels PJ, Sloos JH, van Weert HC. Predicting bacterial cause in infectious conjunctivitis: cohort study on informativeness of combinations of signs and symptoms. BMJ. 2004;329(7459):206-210. doi:10.1136/bmj.38128.631319.AE

10. Everitt HA, Little PS, Smith PW. A randomised controlled trial of management strategies for acute infective conjunctivitis in general practice. BMJ. 2006;333(7563):321. doi:10.1136/bmj.38891.551088.7C

11. Stapleton F, Keay L, Edwards K, et al. The incidence of contact lens-related microbial keratitis in Australia. Ophthalmology. 2008;115(10):1655-1662. doi:10.1016/j.ophtha.2008.04.002

12. U.S. Preventive Services Task Force. Ocular Prophylaxis for Gonococcal Ophthalmia Neonatorum: Preventive Medication. Rockville, MD: Agency for Healthcare Research and Quality; 2019. PMID:30758950

13. Adlard MW, Walters P, Walland M, Jennings L. Epidemic adenoviral conjunctivitis: a persistent public health problem. J Hosp Infect. 2004;57(2):95-100. doi:10.1016/j.jhin.2004.03.004

14. World Health Organization. Trachoma Elimination: WHO Alliance for the Global Elimination of Trachoma by 2020. Geneva: WHO; 2021. Available at: www.who.int/news-room/fact-sheets/detail/trachoma

15. Bielory L, Meltzer EO, Nichols KK, Melton R, Thomas RK, Bartlett JD. An algorithm for the management of allergic conjunctivitis. Allergy Asthma Proc. 2013;34(5):408-420. doi:10.2500/aap.2013.34.3695

16. Epling J. Bacterial conjunctivitis. BMJ Clin Evid. 2012;2012:0704. PMID:22315395

17. Visscher KL, Hutnik CM, Thomas M. Evidence-based treatment of acute infective conjunctivitis: breaking the cycle of antibiotic prescribing. Can Fam Physician. 2009;55(11):1071-1075. PMID:19910590

18. O'Brien TP, Jeng BH, McDonald M, Raizman MB. Acute conjunctivitis: truth and misconceptions. Curr Med Res Opin. 2009;25(8):1953-1961. doi:10.1185/03007990903038269

19. Tabbara KF. Ocular tuberculosis: anterior segment. Int Ophthalmol Clin. 2005;45(2):57-69. doi:10.1097/01.iio.0000155786.69110.b8

20. Jefferis JM, Perera R, Everitt HA, et al. Acute infective conjunctivitis in primary care: who needs antibiotics? An individual patient data meta-analysis. Br J Gen Pract. 2011;61(590):e542-e548. doi:10.3399/bjgp11X593811

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Medical Disclaimer: MedVellum content is for educational purposes and clinical reference. Clinical decisions should account for individual patient circumstances, local guidelines, and current evidence. Always consult appropriate specialists and maintain awareness of evolving best practice. This content is designed for postgraduate medical examination preparation and continuing professional development.